Unlike the respiratory organs of airbreathing vertebrates where gas exchange is perfusion limited, gas transfer across fish gills is diffusion limited. Fish can therefore enhance gas exchange by increasing the gill diffusing capacity. Previous suggestions, indicate that fish may achieve this by altering the pattern of gill blood flow to increase the area of gill perfused and to reduce the blood-water diffusion barrier. To verify these suggestions an investigation of the patterns of gill blood flow, their regulation and their significance in gas exchange in the ling cod, Ophiodori elongatus, was undertaken. The circulatory arrangement in the gill filament of the ling cod consists of an arterio-arterial respiratory network and an arterip-venous veriolymphatic system. All cardiac output passes through the respiratory exchange sites, the lamellae. Blood flow through lamellae is described by sheet blood flow equations, where flow is proportional to the vascular sheet thickness (h). The lamellar vascular sheet is very compliant .and h increases with transmural pressure (ΔP[sub lam]). It is predicted if ΔP[sub lam] and flow are raised, then intralamellar shunting of blood flow and a reduction of the blood-water barrier will result, thereby increasing the gill diffusing capacity; Not all lamellae appear to be equally perfused under certain in vivo conditions. Furthermore, if resting perfusion conditions are simulated, only 67% of the more proximal lamellae are perfused. Thus the total gill area is not utilised at rest. To account for this situation it is proposed that the critical closing pressures associated with distal lamellar units are greater than those for the proximal lamellae. The afferent arterioles were determined to be the major resistance site in the gills and they therefore control flow to lamellae. Elevations in flow and lamellar input pressure will reduce the likelihood of' critical closing and more lamellae will be perfused. Lamellar recruitment increases the gill diffusing capacity. , The demonstrated changes in flow patterns to and within lamellae are effected by elevated flow and input pressures (or ΔP[sub Lam]). Changes in cardiac performance and in the pressure profile of the gills alter flow and pressure. Cardiac performance in ling cod is influenced by intrinsic, cholinergic and adrenergic controls which alter stroke volume and heart rate. The pressure profile of the gills can be altered by cholihergically or adrenergically mediated changes in vessel dimensions. The gill outflow arteries vasoconstrict in localised regions with cholinergic .stimulation and thereby increasing gill resistance (Rg) and lamellar' input pressures. Afferent vessels apparently dilate with-g-adrenergic stimulation and thereby lower Rg. Cardiovascular changes are associated with conditions of reduced oxygen availability (hypoxia) and of increased oxygen demand (struggling) in ling cod. The cardiovascular changes are such that they alter the pattern of gill blood flow and increase the gill diffusing capacity. Increased oxygen uptake, cardiac output and gill ventilation are associated with hypoxia and struggling. The quantitative increases in cardiac output per se associated with these conditions does not fully account for the observed increase in oxygen uptake. It is concluded that change in gill diffusing capacity through alterations in gill blood flow patterns are important in enhancing oxygen uptake across the gills. / Science, Faculty of / Zoology, Department of / Unknown

Indiana University-Purdue University Indianapolis (IUPUI) / A pulsatile flow loop can be suitable for measurement of in vitro blood pressure. The pressure data collected from such a system can be used for evaluating stenosis in human arteries, a condition in which the arterial lumen size is reduced. The objective of this work is to develop an experimental system to simulate blood flow in the human arterial system. This system will measure the in vitro hemodynamics using 3-D prints of vessels extracted from patient CT images. Images are segmented and processed to produce 3-D prints of vessel geometry, which are mounted in the loop. Control of flow and pressure is made possible by the use of components such as a pulsatile heart pump, resistance, and compliance elements. Output data is evaluated by comparison with CFD and invasive measurement. The system is capable of measurement of the pressures such as proximal, Pa, and distal, Pd, pressures to evaluate in vivo conditions and to assess the severity of stenosis. This is determined by use of parameters such as fractional flow reserve (FFR=Pd/Pa) or trans-stenotic pressure gradient (TSPG=Pa-Pd). This can be done on a non-invasive, patient specific basis, to avoid the risk and high cost of invasive measurement. In its operation, the preliminary measurement of blood pressures demonstrates agreement with the invasive measurement as well as the CFD results. These preliminary results are encouraging and can be improved upon by continuing development of the experimental system. A working pulsatile loop has been reached, an initial step taken for continued development. This loop is capable of measuring the flow and pressure from in a 3-D printed artery. Future works will include more life-like material for the artery prints, as well as cadaver vessels.

Recent research was reviewed which claimed to demonstrate that hypnotic suggestions could be used to control blood flow. Numerous methodological and conceptual problems in these studies were identified and a rigid experimental design with tighter controls was employed to investigate the claimed effects on blood flow. Subjects listened to either a standardized hypnotic induction or a passage of relaxing music. Both groups then listened to the Creative Imagination Scale (Wilson & Barber, 1978) (CIS) which ended with an added item containing suggestions of coolness. Localized skin temperature of the right hand was monitored throughout as an indication of blood flow. No significant blood flow increases in response to suggestions of warmth nor decreases in response to suggestions of coolness were observed. The experience of suggested events did not differ significantly between those subjects who received the induction and those who received the passage of music. An increase in blood flow occurred in response to receiving either an induction or music. There was, however, no significant difference between these two groups on the magnitude of the increase. Neither was there a significant difference in this magnitude between high scorers on the CIS and low scorers on the CIS. Results of this and previous studies were discussed within the context of the effects of relaxation as an alternative explanation to the supposed effects of hypnotic suggestion.

No description available.

A new constitutive equation has been developed for the flow of blood through capillaries. Pressure drop and volume flow data of Haynes and Burton and Merrill et al. have beer utilized in this development for a range of radii from 57.04 micra to 747.4 micra and a hematocrit range of 8.8% to 82.5%. A comparison has been made with the Casson equation used by Merrill and Pelletier and the advantage of this new equation over the Casson equation has been verified. The usual assumption of no-slip-at-the-wall has been verified to be valid, up to a hematocrit level of 39.3%. / Thesis / Master of Engineering (ME)

No description available.

Heat stress and dehydration pose a severe challenge to physiological function and the capability to perform physical work. There is, however, limited knowledge on the regional haemodynamic and metabolic responses to strenuous exercise in environmentally stressful conditions. The primary aim of this thesis was to examine whether dehydration and heat stress compromise brain, muscle and systemic blood flow and metabolism, and whether depressed brain and muscle oxygen delivery underpin reduced exercise capacity during graded incremental and prolonged exercise. This thesis makes an original contribution to the knowledge by showing for the first time that dehydration markedly accelerates the decline in cerebral blood flow during maximal incremental (Chapter 4) and prolonged sub-maximal exercise (Chapter 5) in the heat. Cerebral metabolism, however, is preserved by compensatory increases in substrate extraction. Falling carbon dioxide tension underpinned the decline in CBF. However, a distinct regional distribution of blood flow across the head was observed, suggesting that different mechanisms are responsible for the regulation of regional blood flow within the head. A reduced cerebral metabolism is therefore an unlikely factor explaining the compromised exercise capacity in physiologically stressful hot environments. Rather, restrictions in active muscle blood flow and oxygen supply, which are not apparent during sub-maximal exercise, may explain the reduced maximal aerobic power in heat stressed conditions. For the first time we have manipulated skin and core temperature to show that combined internal and skin hyperthermia reduces maximal aerobic power in association with restrictions in limb, brain and systemic blood flow and skeletal muscle metabolism (Chapter 6). Overall, the findings of the present thesis provide novel information on how circulatory limitations across contracting skeletal muscle, brain and systemic tissues and organs might underpin the impairment in exercise capacity in physiologically taxing environments evoking significant dehydration and hyperthermia.

Thesis (M.Sc. (Applied Mathematics)) -- University of Limpopo, 2008 / Understanding the effects of blood viscosity variation plays a very crucial role in hemodynamics, thrombosis and inflammation and could provide useful information for diagnostics and therapy of (cardio) vascular diseases. Blood viscosity, which arises from frictional interactions between all major blood constituents, i.e. plasma, plasma proteins and red blood cells, constitutes blood inherent resistance to flow in the blood vessel. Generally, blood viscosity in large arteries is lower near the vessel wall due to the presence of plasma layer in this peripheral region than the viscosity in the central core region which depends on the hematocrit. In this dissertation, the flow of blood in a large artery is investigated theoretically using the fluid dynamics equations of continuity and momentum. Treating artery as a rigid channel with uniform width and blood as a variable viscosity incompressible Newtonian fluid, the basic flow structure and its stability to small disturbances are examined. A fourth-order eigenvalue problem which reduces to the well known Orr–Sommerfeld equation in some limiting cases is obtained and solved numerically by a spectral collocation technique with expansions in Chebyshev polynomials implemented in MATLAB. Graphical results for the basic flow axial velocity, disturbance growth rate and marginal stability curve are presented and discussed. It is worth pointing out that, a decrease in plasma viscosity near the arterial wall has a stabilizing effect on the flow.

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 114-145). Also available in electronic format on the Internet.

No description available.